Flash photography



Sept. 26, 1944. EDGERTON 2,358,796

FLASH-PHOTOGRAPHY Filed D60. 17, 1941 2 Sheets-Sheet l P 1944- H. E. EDGERTON FLASH-PHOTOGRAPHY Filed Dec. 17, 1941 2 Sheets-Sheet 2 Patented Sept. 26, 1944 UNITED STATES PATENT OFFICE.

FLASH PHOTOGRAPHY Harold Eugene Edger-ton, Belmont, Mass.

Application December 17, 1941, Serial No. 423,344

3 Claims.

The present invention relates to flash-photography, and more particularly to electrical flash-photography in which charged condensers are rapidly discharged through gaseous-discharge flash-lamps.

In the studio, as all conveniences are available, it is possible to supply the power necessary for purposes of such electrical flash-photography from the electrical wiring of the room. In the field, such as in news work, it often occurs that electrical power is unavailable for operating lamps of the above-described character.

An object of the present invention is to improve upon photographic field equipment, in order to enable the field photographer to enjoy the advantages of electrical flash-photography employing gaseous-discharge flash-lamps comparable t those obtaining in the studio.

The use of chemical flash-bulbs has long been recognized as attended with a number of inconveniences resulting from the delay involved in removing one bulb and replacing it by another. Proposals have'therefore been made to employ incandescent bulbs, but they have never been successful and, in fact, have constituted steps backward rather than forward.

Another object of the present invention,.on the other hand, is to provide a fleid system employing gaseous-discharge flash-lamps.

Other and further objects will be explained hereinafter and will be particularly pointed out in the appended claims.

With the above ends in view, a feature of the invention resides in mounting upon a portable field camera an electrically operated gaseousdischarge flash-lamp, in combination with a selfcontained storage battery and a vibrator for converting the power of the battery into alternating current, and with means for reconversion into direct current for charging the condenser. Provision may also be made for operation from an alternating-current source, if desired, and for recharging the battery.

The invention will now be described more fully in connection with the accompanying drawings, in which Fig. 1 is a perspective illustrating a preferred embodiment thereof; Fig. 2 is a simplifled circuit diagram omitting the battery source of energy and its connections; and Fig. 3 is a more complete circuit diagram.

A gaseous-discharge flash-lamp I8 disposed, together with a high-voltage spark trigger-wire or trip-wire flashing electrode I I, in an elongated light-permeable glass-bulb protective jacket or envelope 02, is shown mounted in a reflector 25 upon an arm 53. An external tri gering electrode II, as shown, is necessary with the larger flash-lamps and at the higher voltages. Internal triggering electrodes may, however, be employed with shorter flash-lamps and lower voltages. The flash-lamp I0 may, if desired, be of the helical or spiral gas-filled type disclosed in Letters Patent 2,277,698, issued to Kenneth J. Germeshausen on March 31, 1942, and may be easily interchanged in the reflector 25 by means of a plug-in base 94.

The reflector 25 extends i'orward from a lamp housing 26 to which the upper end of the arm 03 is directly secured. The lamp housing 20 carries a terminal board I00 (shown bydotted lines in Fig. 3) provided with plug receptacles I50, I52 and III, II2 for receiving plugs I02 and I06, respectively. A plug I02, that is adapted to be plugged into the plug receptacles I50, I52, is connected to a camera-shutter synchronization switch S5. A plug I08, that is adapted to be plugged into the plug receptacles III, I12, is connected to the coil of a trip magnet 01. The plugs I02 and I00 may thus be disconnected from the terminal board Illl of the housing 20 on the arm 63 to facilitate packing the equipment in carrying cases. The lower end of the arm 63 is shown attached to the upper wall of a portable camera 35 that may be carried in the fleld-photographers hand.

The bulb 92 containing the flash-lamp Il may, of course, be mounted upon the camera 35 without the reflector 25, but the reflector is espe- \cially desirable for field work, as it helps concentrate the light rays upon the object to be photographed and reduces the size of the flashlamp necessary to be employed.

'The assembly of the flash-lamp I8 and the reflector 25 in which it is housed may be mounted readily on almost any type of camera by means of the arm 63. The reflector 25 may be so oriented upon the camera 2! as automatically to illuminate the area desired to be photographed with relative uniformity at the moment of the exposure flash. The reflector may be adjusted, for spot or flood lighting, by means of a knob I on the back of the lamp housing 26.

The flash-lamp I8 is controlled by a control circuit that is disposed, with a power unit and other apparatus, in a box I that may be carried over the field-photographers shoulder by means of a. shoulder strap 43. The box 4|, power-unit and all, may weigh only twenty pounds. It may be nine inches long, five inches wide, and nine inches high. The box II contains apparatus and circuits diagrammatically indicated within the dotted-line outline ll of Fig. 3, and described more fully hereinafter. The flashlamp I8 and its connecting parts may be connected to, and disconnected from, the powerunit box 4| by means of a connector plug 55 that may be connected into an outlet connection 51 provided in the wall of the box 4|. A sixfoot cord 89 for containing the wiring is shown permanently attached to the lamp house 23 at one end and to the plug 55 at the other. complete self-contained portable equipment is thus provided, that may be carried from place to place for photographing any object anywhere.

The control circuit contains a flash condenser II, across which the flash-lamp I8 is connected. The exposure flash is produced by discharging the condenser II through the flash-lamp I8, in response to suitable energization of the trip-wire electrode I 1, by means of a flash-lamp triggering circuit more fully described hereinafter. The discharge circuit for the condenser II through the flash-lamp I8 may be traced from a grounded terminal I5, at one side of the condenser II, by way of a conductor 3i, through the connection 51 and the flash-lamp I8, and by way of a conductor 20, through the connection 51, to the other side of the condenserv I I.

A suitable source of direct-current energy must, of course, be provided for charging the condenser II. As the instrument must be portable, no reliance can be placed upon outside sources of current. According to a feature of the invention, a small spill-proof lead storage battery 69, which may be of four volts, may be provided for operating the flash-lamp I8. This is small enough so as not to interfere with the portability of the instrument.

As a source of alternating-current energy or its equivalent is also needed, a vibrator inverter 39 is added, connected to a high-ratio step-up transformer 05, provided with a primary winding 41 and a secondary winding 09. The primary winding 41 is connected to the battery 59 through the vibrator 39. The voltage of the battery 69 is thus converted in the primary winding 01 into an interrupted or pulsating chopped wave, which is stepped up in the secondary winding 43.

The secondary winding 09 is connected to the condenser I I through a rectifier 12. The steppedup pulsating wave in the secondary winding 09 becomes thus converted into direct current for charging the flashing condenser II. If the secondary winding 49 has a high impedance, it may perform also the current-limiting function for which a separate charging resistor or other impedance is normally supplied between the secondary winding 49 and the charging condenser I I.

Energy from the battery 69 is thus supplied to the flashing condenser II, to charge the same, through the transformer 45. Energy from the same battery 69 may be provided for heating the cathode 19 of the rectifier 12. To this end, the cathode 19 may be connected by conductors Ill and I23 in circuit with a winding 83 that constitutes a further secondary winding for the primary winding 41 of the transformer 45.

If a suitable source of alternating current, such as the ordinary 110-volt, 60-cycle house mains, is available, however, the condenser I I may be charged therefrom by plugging at 1|. This may be effected by disconnecting the battery 69, even removing it altogether, if desired. The plug H is connected by input wires 13 to a jack 13 which, in turn, is connected to the secondary winding 49 of the same transformer 45, but employing a different primary winding 15. The Jack 16 is connected by conductors I33 and I31 to the primary winding 15.

A condenser I35 is connected to the transformer to aid the vibrator during commutation by changing the power factor. Sparking at the vibrator contacts is thereby reduced.

A large-enough condenser II should be employed so as to impress sufficient power, under suitable voltage, between the cathode and the anode of the flash-lamp. There is no difliculty, through the medium of this apparatus, charging the condenser II to a voltage of, say, 2000 volts. At this voltage, a condenser of 28 microfarads is very efiicient.

A normally non-conducting gaseous-discharge trigger tube I for tripping the flash-lamp I8 may be connected to terminals I5 and I3, across an impedance 8|, shown as a bleeder resistor. The bleeder resistor 81 is connected, in series with a bleeder resistor 82, across the condenser I I, which thus, by supplying energy to the bleeder resistor 8|, constitutes the main power-supply for the tube I. The resistors 8I and 82 may be so proportioned that a desired voltage of, say, 300 volts shall appear across the terminals I3 and I5 of the resistor BI.

The tube I may be of the cold-cathode gaseousdischarge type illustrated and described in Letters Patent 2,185,189, 2,201,166 and 2,201,167, issued to the said Kenneth J. Germeshausen, on January 2, 1940, and May 21, 1940. It may comprise an evacuated glass envelope containing several electrodes, namely, a solid cathode 2, an anode or plate 5, and one or more grids, inner and outer grids being shown at 3 and 3, between the anode 5 and the cathode 2. As explained in the said Letters Patent, the source of the electrons is a bright cathode spot on the surface of the oathode 2. Part of the impedance 89 is shown connected between the cathode 2 and the grid 41. The cathode 2 and the grid 3 may be connected together with or without a further impedance not shown) between them.

A trigger-discharge circuit for a condenser 10 is also connected to the terminals I3 and I5, in parallel with the tube I. One side of the condenser 10 is connected in this discharge circuit to the terminal I3. The other side of the condenser 30 is connected, by way of a conductor 90, to the primary winding 1 of a transformer 36 and, by way of the conductor 21, to the ground terminal l5. The condenser 60 is thus connected in this discharge circuit in series with the primary winding 14. One side of the secondary winding 38 of the transformer 36 is grounded to the terminal I5 by way of the conductor 21, and the other side is connected, by a conductor 31, to the trip-electrode I1. A return path is afforded by capacity coupling of the trip-wire electrode I1 to the flash-lamp I8. The condenser 40, therefore, becomes charged from the same directcurrent source 45, 12, a the condenser II, through the resistor 8| and the primary winding 14. The flashing circuit thus contain the flashlamp I8 and the secondary winding 38, which opcrates as an induction coil. I

A hand-controlled push-button switch 53 is shown in Fig. 1 mounted upon the box 4|. The switch 53 is shown in Figs. 2 and 3 connected across the anode or plate 5 and the grid or control electrode 4, through a trip condenser 93 and a leak resistor 91, in parallel, by way of conductors 9| and 93. At any time after the directcurrent source 45, 12, charges the condenser II to its maximum value, the push-button switch It may be closed. The potential of the grid 4 will then become raised until the break-down voltage between the grid 4 and the cathode 2, or the grid 4 and the grid 3. is exceeded, whereupon the normally ineffective trigger-tube I becomes effective by being rendered conducting. Current then flows through the trigger tube I, causing the gerlng spark through the flash-lamp I8 will yield a very brilliant exposure flash of extremely short duration. The time taken between the closing of the push-button switch 53 and the flash of light from the flash-lamp I8 is very brief. It is therefore possible to produce this very brilliant flash of light at any desired instant for taking photographs. When the condenser II is fully discharged, the flash-lamp III extinguishes, and the cycle is ready for repetition.

The operation of the synchronization switch 65 is effected in timed relation to the flashing of the flash-bulb I8 under the control of the pushbutton-switch 53. To this end, th plug receptacles I50 and I52, to which the synchronizing switch 65 is connected by the plug I02, are connected in parallel to the anode 5 and the control electrode 4. The connection may be traced from the conductor 9|, that is connected to one side of the push-button switch 53 and to the control electrode 4, and by way of a conductor 5, through the connector 51, to th plug receptacle I52; and from the conductor 93, that is connected to the other side of the push-button switch 53 and to the anode 5, by way of the conductor 21, and through the connector 51, to the plug receptacle I50. The lamp I8 may thus be synchronized to flash at a time when the shutter is open. This is arranged by the use of a contact point which is operated when the shutter 66 is open. This may be either external or internal but is operated by the mechanismthat opens the leaves of the shutter.

The shutter 56 may be operated independently of the push-button switch 53 by means of a pushbutton switch 5|, that controls the coil of the trip magnet 51. The shutter may also be operated manually, or with the usual cable release. A illustrated in Figs. 2 and 3, the battery 69 is connected to the tripcoil 61 by the closing of the switch 5i. The connections may be traced from the negative and of the battery 69, by way of the conductor Il, through the connector 51, to th push-button switch then through the receptacle I11 and the plug I06, the trip coil 51,

and the receptacle I12 and the plug I06, by way of a conductor 8 and conductor 3|. to the grounded positive terminal of the battery 69.

The flash-lamp It should have characteristics such as to produce an extremely rapid exposure. The rapidity of the exposure produced with the hereinafter described flash-lamp, indeed, far exceeds that of the fastest camera shutter.

pressure of the gas in the tube, all are factors I that determine the brightness oi the flash. The influence of the dimensions will be understood when it i reflected that if the flash-lamp I I is short, there will not be so much resistance between its cathode and its anode, through the gas in the tube, as when the lamp is large. The increased resistance produced by a long tube may have the same effect as the increased power afforded by a proper-size condenser.

The gap length, between the electrodes of the flash-lamp I0, may preferably be about 10 to 12 inches. It may, however, be longer, even as long as sixty inches. The diameter of the arc path also influences the effective resistance 01' the flash-lamp. If this diameter is reduced, the resistance of the lamp becomes increased. Under some conditions, more light is then produced. The internal diameter of the flash-lamp I8 may preferably be about to a! of an inch, but it may be as low as V; inch and as large as /3 of an inch. In general terms, it may he stated that the length of the lamp should be at least ten times as long as its diameter.

The pressure of the gas in the flash-lamp depends, to some extent, upon the voltage. At higher voltages, speaking generally, either the gas pressure must be raised, or else the flashlamp must be made longer. The lower the voltage, on the other hand, the shorter may be the length of the flash-lamp, or the lower may be the gas pressure. The diameter need not be substantially changed in response to these variations. The voltage may be as low as between about 200 or 300 volts, though a voltage as low as volts has been used. The upper voltage limit may vary with the gas pressure and the length of the flashlamp. Some particular types of flash-lamp will easily operate above 3000 volts.

Good results have been obtained at a gas pressure of 5 centimeters, but h gher pressures have been used, even almost up to atmospheric. At 2000 volts, a pressure from 2 /2 to 10 centi meters is workable.

There are also other factors, which can not be expressed mathematically. yet which have a bearing upon the efficient operation of the instrument. In a high-pressure lamp, the ionized vapor does not deionize at a rapid enough rate to produce a practical light-source at high frequency. The flash-lamp must not be permitted to become heated up too much; for if the lamp is operated at too high a temperature, it may either fail to ignite or, on the other hand. its arc may degenerate into a continuous glow. with only a very small-intensity consequently attendant continuous light. The voltage of the condenser II and the other factors before discussed should be properly chosen to prevent this happemng.

The dimensions of the tube have a bearing also in connection with the temperature at which the lamp is operated. Very large tubes have a tendency to become automatically cooled between flashes. Itis desirable that the ratio of the total over-all energy input to the ratio of the tube dimensions be maintained to an extent sufficient to produce proper flashing for stroboscopic or other purposes.

The gas contained in the flash-lamp l8 may be krypton, but other gases are also suitable, particularly argon and xenon.

One advantage of employing krypton, argon and xenon as the gas fllling or the tube is that the pressure of these gases does not change so rapidly with temperature as do other gases, like mercury vapor. This enables the lamp to be operated with high efllciency both when cold and when hot..

The volume of light of the exposure flash produced by the lamp I8 makes possible the use of small camera apertures with a resulting great depth of field. The flashes are unaccompanied, however, by eye discomfort, due to the color and shortness of the flashes.

Owing to its freedom from dependence on external lighting circuits, and the great capacity of the instrument before recharging the battery 99, the present invention makes it possible for the photographer to roam about, taking flash aiter flash, without taking heed to anything except pressing the shutter or the button at the proper time. He is assured that he will have ample illumination to obtain natural, critically sharp photographs of large objects and small, whether stationary or moving at high speed, and all of equal photographic quality, as the flashes produced by the successive battery charges are of uniform intensity and volume. He may employ about any ordinary camera: The only necessary addition to his camera 35 is the flash-lamp I8, with or without the reflector 25 in which it is disposed, mounted on the camera, and the power unit contained in the box 9|.

The power unit is shown provided with a further outlet 59 for connecting a second flash-lamp M, where it is desired to obtain side lighting, as is sometimes desired in the field. The flashlamp 9| may be connected in parallel to the flash-lamp I3, as illustrated in Fig. 3, and described more fully in a copending application, Serial No. 421,931, flled December 6, 1941. The parallel-connected wires may be contained in a fifteen-foot cord 30, connected at one end to the outlet 59 andat the other to a second lamp house 69 mounted upon a bracket. Reference numerals applied to the connections and other parts related to the flash-lamp BI are the same as those described above, but augmented by 200. The reflector, for example, is shown at 225.

Provision has been made in the panel for venting' the gases to the outside. The battery can be changed quite readily, since the terminals are accessible.

An electrical battery voltmeter 29 is provided on the top of the power unit for reading the voltage of the battery.

A four-position switch 81 on the top of the power-unit box ll provides the following methods of operation: (1) ofl, (2) battery operation, (3) A. C. operation, (4) battery charge. The description above of the operation has been made on the assumption that the switch 81 occupies the battery-operation position.

The four-position switch 91 is provided with a shaft 44, integrally carrying four switch-arms I6, I2, I0 and I9, each adapted to occupy the four positions before mentioned. These switch arms are each adapted to engage four contact members in the respective four positions. Not all these contact members, however, are effective to make connections.

In the off position, all four switch arms I6, I2, III and I9 engage respective contact members for opening all the circuits. In the "of!" position, accordingly, the circuits are all open.

In the battery-operation" position, the switch arms I9 and I 9 engage open-circuit contact members, thus disconnecting a full-wave copper-oxide rectifier I45, at the switch arm I9, and the input plug II, at the switch arm I9. The switch arm I2, however, engages a contact member I I9 and the switch arm in engages a contact member I98. In the battery-operation" position, therefore, two connections are made. One connection completes a circuit from the negative terminal of the battery 69, by way of conductors IIII and lil, through the switch arm I0 of-the switch 81, the contact member I03 in contact therewith in this position and, by way of a conductor I95, to the vibrating member of the vibrator inverter 39. The stationary members of the vibrator inverter 89 are connected by conductors I01 and I99 to different taps of the primary winding 91. An intermediate tap III is connected by a conductor II3 to the grounded positive terminal of the battery 69. One of the com nections completed in this position of the switch 91, therefore, is from the battery 69 to the primary winding 41 of the transformer 45, through the vibrator inverter 39. A magnet coil II 5 causes the vibrator 39 to vibrate. The other connection made in this position of the switch 91 is to close a circuit for the cathode 19 of the rectifier 12 through a portion of the secondary winding 83, energized, as before described, from the same transformer primary winding 41. The circuit may be traced from the grounded terminal I5, connected to one side of the oathode '19, by way of the conductor II1, through the switch arm I2 of the switch 81, and the contact member 9 in contact therewith in this position of the switch 81, to a tap I2I of the secondary winding 83. The circuit continues through the major portion of the secodnary winding 93, by way of the conductor I23, to the other side of the cathode 19. In this battery-operation" position of the switch 81, therefore, the battery 89 is connected to the primary winding 41 to charge the condensers II and 40, and to heat the cathode 19 of the rectifier 12.

In the position marked "A-C operation, the switch arms I0 and I9 engage open-circuit contact members, the switch arm I9 engages a contact member I3I, and the switch arm I2 engages a contact member I25. The contact member I25 connects the complete secondary winding 99 to the cathode 19 by a circuit extending from the terminal I5, by way of the conductor II1, through the switch arm I2 of the switch 81 and the contact member I25 at this time in contact therewith, by way of a conductor I21, through the secondary winding 83, and by way of the conductor I23, to the cathode 19. The secondary windings 49 and 83 are then supplied with energy, through the further primary winding 15, from the alternating-current mains, through a connection made by the plug II and the wires 13. The connection may be traced from one terminal of the mains, by way of a conductor I29, the switch arm I6 01 the switch 81 and the contact member I3I at this time in contact therewith, by way of a conductor I33, through the primary winding 15 and the condenser I35 in parallel and, by way of a. conductor I31, back to the other side of the mains. In this position of the switch 81, therefore, the battery 89 is disconnected from the primary winding 41, and the instrument is operated by alternating current.

When the switch 91 occupies its "batterycharge" position, the same transformer 45 may be employed to recharge the battery 69, through the copper-oxide rectifier I45, from any source oi alternating current, such as any of the standard 1l0-volt alternating-current outlets. This may be eifected with the aid of a built-in selfcontained full-wave-rectifying trickle charger.

Recharging is not ordinarily necessary until after some two hundred consecutive exposure flashes, corresponding to four hours of continuous use, which permits a very large program.

In the position marked "battery charge, the switch arm I2 is open-circuited to disconnect completely the cathode 19. The primary winding 15 is connected to the altemating-current mains in the same way as before described, ex cept that the switch arm I5 of the switch 81 makes contact, not with the contact member I3 I, but with a contact member I39 which, being permanently connected to the contact member I3I, is likewise connected to the conductor I33. At this time, the switch arms III and I9 of the switch 81 make contact with contact members HI and I43, respectively. Both contact members I and I43 are connected to the rectifier I45 and, through this rectifier, to the primary winding 41 of the transformer 45. The contact member I43 connects the full-wave copper-oxide rectifier I45 to opposite terminals of the primary winding 41, which is at this time supplied with energy, through the primary winding 15, from the alternating current mains. One end of the copper-oxide rectifier is connected to one end of the transformer winding 41 by a conductor I41. The other end of the full-wave rectifier is connected to the other end of the transformer winding 41 through the switch arm I5 of the switch 81 and the contact member I45 at this time in contact therewith, by way of a conductor 20.

The intermediate tap III of the transformer winding 41 is connected, as before stated, by the conductor M3 to the grounded positive terminal of the battery 59. The negative terminal of the battery 58 is connected, by way of the conductors NH and IN, the switch arm III of the switch 81 and the contact member I4I in contact therewith in this position of the switch 81, and by way of the conductor I55 to an intermediate point of the full-wave rectifier I45. By reason of these connections, the energy supplied to the transformer winding 41 by the primary winding from the alternating-current mains is utilized in alternate cycles, through opposite halves of the winding 41 and corresponding portions of the full-wave rectifier I45, to charge the battery.

The battery-charging is thus eflected when the switch is set at the battery-charge position. A charging rate of about one ampere is used, which charges the battery in eight to ten hours. The battery is easily inspected by removing ,a panel on the side of the box,

Modifications will occur to persons skilled in theartandallsuchareeonsideredtofallwithin the spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

1. Apparatus for use in flash-photography having, in combination, a camera. a gaseous-discharge flash-lamp mounted on the camera, a condenser connected to the flash-lamp to effect a discharge through the flash-lamp to produce an exposure flash, a battery, a vibrator, a transformer having a primary winding and a secondary winding, means for connecting the primary winding to the battery through the vibrator, means for connecting the secondary winding to the condenser to charge the condenser, a second transformer having a second primary winding and the said secondary winding, means for connecting the second primary winding to a source of 'altemating current at a time when the first-named primary winding is disconnected from the battery, and means for constituting the first-named primary winding as a secondary winding to the primary winding of the second transformer to charge the battery.

2. Apparatus for use in flash-photography having, in combination, a camera, a gaseous-discharge fiash-lamp mounted on the camera, a condenser connected to the flash-lamp to effect a discharge through the flash-lamp to produce an exposure flash, a battery, a vibrator, a rectifier having a cathode, a transformer having a primary winding and two secondary windings, means for connecting the primary winding to the battery through the vibrator, means for connecting one of the secondary windings to the cathode to energize the cathode, means for connecting the other secondary winding t0 the condenser through the rectifier, a second transformer having a second primary winding and the said secondary windings, means for connecting the second primary winding to a source of alternating current at a time when the first-named primary winding is disconnected from the battery, a full-wave rectifier, means for connecting the first-named primary winding through the full-wave rectifier to the battery, and means for connecting the first-named primary winding to the second primary winding to charge the batt ry.

3. Apparatus for use in flash-photography having, in combination, a camera, a gaseousdischarge flash-lamp mounted on the camera, a battery, a vibrator, a transformer, a four-position switch in one position of which the circuits are disconnected, means operable when the switch occupies a second position for connectins the transformer to the battery through the vibrator to produce an exposure flash through the gaseous-discharge flash-lamp, means operable when the switch occupies a third position for effecting an exposure flash through the flashlamp from a source of alternating-current energy, and means operable when the switch occupies its fourth position to connect the transformer to the source of altemating-current energy to charge the battery.

HAROLD E. EDGERTON. 

